I fixed this by deleting the visual studio solution user options file (.suo) and then restarting VS.
UPDATE: For VS 2017, you need to delete a hidden folder named .vs located in solution directory (Thanks @Tien Dinh!)
I fixed this by deleting the visual studio solution user options file (.suo) and then restarting VS.
UPDATE: For VS 2017, you need to delete a hidden folder named .vs located in solution directory (Thanks @Tien Dinh!)